Multicenter Interventional Lymphangioleiomyomatosis Early Disease Trial (The MILED Trial) Project Summary Lymphangioleiomyomatosis (LAM) is low-grade metastasizing neoplasm of women, driven by activating mutations in the mTOR pathway that result in cystic destruction of the lung. The benign appearing, mutation bearing smooth muscle-like LAM cells that infiltrate the lung arise from an unknown source and execute a program of matrix remodeling that leads to cyst formation, recurrent pneumothorax, chylous pleural effusion and progressive respiratory failure. There has been tremendous progress in LAM in the past decade, including a rich molecular understanding of disease pathogenesis, development of a diagnostic and prognostic biomarker, and the discovery of a treatment. The randomized controlled Rare Lung Disease Consortium (RLDC) Multicenter International LAM Efficacy of Sirolimus (MILES) Trial (Sponsor-FXM, IND 71,340) demonstrated that mTOR inhibition with sirolimus is an effective suppressive therapy for LAM, stabilizing lung function, functional performance, and quality of life in women with abnormal lung function. Side effects due to sirolimus were common in MILES, although SAEs were balanced in the sirolimus and placebo groups. The beneficial effects of sirolimus waned when the drug was held in the second year of the trial. Although the primary eligibility criterion was forced expiratory volume in 1 second (FEV1) ? 70%, enrolled MILES patients had more advanced respiratory impairment, with about half of lung function remaining (on average), limiting the generalizability of the findings to mild disease. Fear of toxicities and life long therapy lead most clinicians and patients to wait until lung function becomes abnormal before initiating sirolimus therapy to stabilize the damaged lung. This approach is suboptimal and inadequate. The Multicenter Interventional LAM Early Disease Trial (MILED) is a phase III, randomized, placebo-controlled trial to determine if early, long term (2 yr), low dose (1 mg/day) sirolimus treatment of patients with well-preserved lung function will safely prevent disease progression. Sixty patients with normal FEV1 (FEV1>70%) will be enrolled and randomized to 1 mg/day sirolimus or placebo, and followed for 2 years with pulmonary function testing every 4 months. The primary endpoint will be the between-group (placebo vs. sirolimus) difference in the rate of change in FEV1 (in liters). Secondary endpoints will include between group differences in adverse events, forced vital capacity, lung volumes, diffusing capacity, serum VEGF-D, and early airflow obstruction assessed using hyper-polarized gas MRI. The study will be conducted using the infrastructure created for the RLDC, using the Rare Lung Disease Clinic Network, which is currently following over 1200 U.S. LAM patients and conducting the TRAIL trial. The LAM Foundation will be an integral partner and will assist with study recruitment and patient participation. Data will be managed by the University of South Florida Data Management and Coordinating Center. Successful completion of these aims will define the safety and efficacy of low dose sirolimus in patients with normal lung function, and determine if sirolimus can be used to prevent disease progression to symptomatic stages.